[PATCH RESEND] io_uring/af_unix: disable sending io_uring over sockets

[Pavel Begunkov <asml.silence@gmail.com>]

File reference cycles have caused lots of problems for io_uring
in the past, and it still doesn't work exactly right and races with
unix_stream_read_generic(). The safest fix would be to completely
disallow sending io_uring files via sockets via SCM_RIGHT, so there
are no possible cycles invloving registered files and thus rendering
SCM accounting on the io_uring side unnecessary.

Cc: stable@vger.kernel.org
Fixes: 0091bfc81741b ("io_uring/af_unix: defer registered files gc to io_uring release")
Reported-and-suggested-by: Jann Horn <jannh@google.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---

Note, it's a minimal patch intended for backporting, all the leftovers
will be cleaned up separately.

 io_uring/rsrc.h | 7 -------
 net/core/scm.c  | 6 ++++++
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/io_uring/rsrc.h b/io_uring/rsrc.h
index 8625181fb87a..08ac0d8e07ef 100644
--- a/io_uring/rsrc.h
+++ b/io_uring/rsrc.h
@@ -77,17 +77,10 @@ int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 
 int __io_scm_file_account(struct io_ring_ctx *ctx, struct file *file);
 
-#if defined(CONFIG_UNIX)
-static inline bool io_file_need_scm(struct file *filp)
-{
-	return !!unix_get_socket(filp);
-}
-#else
 static inline bool io_file_need_scm(struct file *filp)
 {
 	return false;
 }
-#endif
 
 static inline int io_scm_file_account(struct io_ring_ctx *ctx,
 				      struct file *file)
diff --git a/net/core/scm.c b/net/core/scm.c
index 880027ecf516..7dc47c17d863 100644
--- a/net/core/scm.c
+++ b/net/core/scm.c
@@ -26,6 +26,7 @@
 #include <linux/nsproxy.h>
 #include <linux/slab.h>
 #include <linux/errqueue.h>
+#include <linux/io_uring.h>
 
 #include <linux/uaccess.h>
 
@@ -103,6 +104,11 @@ static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
 
 		if (fd < 0 || !(file = fget_raw(fd)))
 			return -EBADF;
+		/* don't allow io_uring files */
+		if (io_uring_get_socket(file)) {
+			fput(file);
+			return -EINVAL;
+		}
 		*fpp++ = file;
 		fpl->count++;
 	}
-- 
2.43.0